The invention disclosed herein is employed in the field of thoracic surgery, whose purpose is to improve the pleural aspiration to which patients are subject during the postoperative stage of such surgery.
Whenever the pleural cavity is opened during a surgery, due to a traumatism or for any other reason, there is a need to leave one or more one-way drainages that will permit the exit of liquids (blood, pus, etc.) and air from lung injuries and will avoid the entrance of ambient air into the pleural cavity. This one-way drainage generally comprises (FIG. 1a) a bottle with a certain quantity of liquid wherein the end of a rigid tube connected to the outside end of a rubber, or plastic tube previously inserted in the pleural cavity, is submerged. The system operates as a one-way valve, as it permits the exit of the pleural contents, while the liquid prevents the entrance of ambient air into the pleural cavity. The efficacy of this type of pleural drainage is limited and it is often desirable to connect it to a vacuum source in order to improve its performance.
Due to functional conditions, the organs contained in the thoracic cavity do not tolerate being subject during a certain period of time, to vacuum or negative pressures over 30 cms of water, without experiencing severe disorders in the cardio-respiratory function. For similar reasons, the intrapleural vacuum must not suffer any important variation; thus intrapleural negative pressures must remain within a narrow range.
The conditions referred to above are achieved by putting an adjustment system between the drainage bottle and the vacuum source. The conventional design comprises a transparent bottle, about 35 cms. high and over 1 liter in volume, having a scale graded in cms. in order to measure the level of the liquid that will be placed inside. The cap of said bottle is crossed by a T-tube, one of which arms is connected to the patient""s pleural drainage bottle and the other one, to the vacuum source (3). A long transparent tube (4) in turn goes through the bottle cap and reaches the bottom of the bottle thus communicating inside with the atmospheric air.
The bottle is filled with water up to the height in cms. that corresponds to the desired negative pressure (5).
When the adjusting bottle is connected to the aspiration system, (FIG. 2), vacuum is attained in the air chamber, which exists in the top end of the bottle (6). When the negative pressures in the air chamber and in the pleural cavity, both being communicated through the drainage tube exceed the vacuum needed to overcome the pressure exerted by the water column located inside the tube (4), the air starts bubbling through the lower end of said tube (FIG. 2). The vacuum source sucks air from the space located at the upper end of the bottle, preventing the pressure from exceeding the fixed limit, the vacuum level thus remaining constant.
There are many designs of this system, most of which have one or several drawbacks which shall be pointed out.
The equipment described are bulky and heavy, their packaging, transport and storage thus being complicated. Because of this characteristic, they are frequently not available when they are needed. This happens mainly in emergency situations, during catastrophes or in field hospitals.
The head of the vessel, due to its structural complexity is made of metal. Consequently, prices are high.
When a significant aerorhage or air leak in the lungs occurs (air coming out of the lung), the air that bubbles in the liquid of the draining bottle, rich in proteins (from the blood or exudates from the pleural cavity), causes abundant foam which, when it is aspirated, partly falls within the adjusting bottle, polluting and/or contaminating the liquid therein. The remaining foam is aspirated into the inside of the vacuum system (FIG. 3). In such cases, the procedure must be suspended, and the apparatus disassembled, cleaned and re-sterilized. The liquid that accidentally entered the vacuum circuit can cause failures in the mechanism, unless a second trap bottle is placed between the adjusting bottle and the circuit.
When the level of liquid in the adjusting bottle is high and air is strongly bubbling, the bubbles reach the lower end of the tube (1) (FIG. 4), water is aspirated by the circuit, with similar consequences as in above item 3.
Another consequence of this fact, is that the level of aspirated water decreases within the bottle, which changes the aspiration conditions.
In order to avoid such drawbacks, a close surveillance on the operation of the device by trained personnel is required, excluding them from functions more important than controlling a bottle wherein air is bubbling.
The tube that communicates the inside of the bottle with the outside is fixed to the cap at one of its ends, while the other end is free. This fact causes this tube to be frequently broken when the bottle is jostled and then the apparatus becomes useless. There are designs having a special device in order to fix the free end of the tube. This expediency makes the manufacturing process more expensive and complicates the assembling process after each cleaning.
Cleaning, sterilization and maintenance of these apparatus is troublesome because the apparatus must be disassembled and subsequently perfectly adjusted in order to prevent water or vacuum leakages. Such a procedure is necessary whenever the apparatus must be stored after usage or has been contaminated by the pleural contents.
The constant bubbling of air in the liquid causes the evaporation of the latter. This leads to the need of regularly controlling the liquid level and replacing it with a certain frequency, adding one more factor to take care of the system.